This invention relates to solution polymerization. In one of its aspects this invention relates to the production of solution rubber polymers. In another of its aspects this invention relates to the recovery of polymers from a solution polymerization process.
Most solution polymerization processes such as that disclosed in U.S. Pat. No. 3,462,347 use a hydrocarbon such as n-hexane, cyclohexane or toluene as a reaction solvent medium. In the recovery of product, the reactor effluent is usually flash concentrated, followed by steam stripping to remove the balance of the solvent, with final recovery of the product as a crumb in water slurry. In such a process the solvent recovered by steam stripping must be dried before it can be recycled to the reactor.
It has also recently been a practice, as shown in U.S. Pat. No. 3,725,377, to purify low concentration monomers by hydrogenation and adsorption so that the use of extensive fractionation and extractive distillation can be avoided in purifying monomers. This has provided a more economical feedstock for polymer production, particularly in the production of solution rubber.
Up to now, it has not been generally recognized that the presence of substantially inert light hydrocarbons in the feed to the reactor in the polymerization of diolefins can have two important advantages in subsequent solvent removal: (1) the presence of inert light hydrocarbons can allow the reaction operator to remove or "back out" part of the reactor solvent but maintain operation of a solution polymerization reactor at the same polymer solids concentration using a reduced amount of heavier hydrocarbon solvent, and (2), because the inert light hydrocarbons are both more volatile and have a lower latent heat of evaporization than the heavier hydrocarbons used as solvent, the reactor effluent can be flashed to a higher polymer concentration so that the amount of solvent to be removed in the subsequent energy intensive steam stripping step can be reduced.
It is therefore an object of this invention to provide a method for producing solution polymerized polymer that uses less energy in the solvent removal step than processes presently employed. It is another object of this invention to provide a solution polymerization method that facilitates the concentration of polymer in the reaction effluent.
Other aspects, objects, and the various advantages of this invention will become apparent upon reading this specification, studying the drawing, and reading the appended claims.